Internal combustion engine ignition system

ABSTRACT

An internal combustion engine ignition system of the inductive type which provides a rapid rise time ignition spark potential and a long duration arc. The primary winding of the ignition coil has an inductance valve which, with a specific energizing current, will provide sufficient stored energy to maintain an ignition arc for a predetermined duration, of the order of 800 microseconds, for example. The ignition coil secondary to primary turns ratio is selected to be of the order of 60:1 to provide a predetermined rise time of the ignition spark potential, of the order of 40 microseconds, for example. To prevent the destruction of the ignition coil primary winding energizing circuit switching device in the event of an open secondary winding output circuit, a metal oxide varistor is connected in shunt across the current carrying elements thereof.

United States I Patent Campbell et al.

3,824,977 July 23, 1974 INTERNAL COMBUSTION ENGINE IGNITION SYSTEM [75] Inventors: Robert E. Campbell; Lewis R.

Hetzler; Gerald 0. Huntzinger, all of Anderson, Ind.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Nov. 23, 1973 [21] Appl. No.: 418,248

[52] US. Cl. 123/148 E, 315/209 [51 Int. Cl. F02p 3/02 [58] Field of Search 123/148; 315/209 [56] References Cited UNITED STATES PATENTS 3,196,313 7/1965 Quinn 123/148 E 3,476,097 ll/1969 Pushton 123/148 E 3,605,713 9/1971 LeMastcrs et al 123/148 E Primary Examiner-Laurence M. Goodridge Assistant Examiner-James W. Cranson, Jr. Attorney, Agent, or Firm-Richard G. Stahr [5 7 ABSTRACT An internal combustion engine ignition system of the inductive type which provides a rapid rise time ignition spark potential and a long duration arc. The pri' mary winding of the ignition coil has an inductance valve which, with a specific energizing current, will provide sufficient stored energy to maintain an ignition are for a predetermined duration, of the order of 800 microseconds, for example. The ignition coil secondary to primary turns ratio is selected to be of the order of 60:1 to provide a predetermined rise time of the ignition spark potential, of the order of 40 microseconds, for example. To prevent the destruction of the ignition coil primary winding energizing circuit switching device in the event of an open secondary winding output circuit, a metal oxide varistor is connected in shunt across the current carrying elements thereof.

5 Claims, 3 Drawing Figures INTERNAL COMBUSTION ENGINE IGNITION SYSTEM This invention is directed to an internal combustion engine ignition system and, more specifically, to an internal combustion engine ignition system of the inductive type which provides a fast rise time ignition spark potential and a long burn ignition arc.

To reliably fire and substantially reduce the incidence of fouled spark plugs, a fast rise time ignition spark potential is required and recent studies indicate that a long burn ignition arc provides improved fuel economy, automobile drivability and engine idling characteristics. Because of practical ignition system parameter limitations, it has heretofore seldom, if ever, been possible to provide an ignition system having both fast rise time ignition spark potential and long burn ignition arc capabilities. For example, it has traditionally been impossible to provide an inductive type ignition system having fast rise time ignition spark potential capability for the reason that intolerably high ignition coil primary winding potential levels may occur during some conditions of operation. These intolerably high ignition coil primary winding potential levels may destroy the ignition coil or the ignition coil primary winding energizing circuit switching device. Consequently, it has heretofore been necessary to design the ignition coil with a secondary winding to primary winding turns ratio sufficiently high to prevent intolerably high primary winding reflected potentials.

The modern trend is to electronic automotive ignition systems which employ transistor switching devices in the ignition coil primary winding energizing circuit for establishing and interrupting the ignition coil primary winding energizing circuit in timed relationship with the engine. Transistor devices are particularly vulnerable to excessive ignition coil primary winding potential levels which may, and probably will, instantly destroy them. The provision of an internal combustion engine ignition system which provides a rapid rise time ignition spark potential and a long burn ignition are without intolerably high ignition coil primary winding reflected potentials under certain operating conditions such as an open secondary winding output circuit, is desirable.

It is, therefore, an object of this invention to provide an improved internal combustion engine ignition system.

It is another object of the invention to provide an improved internal combustion engine ignition system of the inductive type.

It is a further object of this invention to provide an improved internal combustion engine ignition system which provides both a rapid rise time ignition spark potential and a long burn ignition arc without excessive ignition coil primary winding reflected potentials.

In accordance with this invention, an improved internal combustion engine ignition system is provided which supplies both a rapid rise time ignition spark potential and a long burn ignition arc without excessive ignition coil primary winding reflected potentials wherein the ignition coil has a primary winding inductance value sufficiently high to provide a long burn ignition arc and a primary winding to secondary winding turns ratio .low enough to provide a rapid rise time ignition spark potential in combination with a metal oxide varistor potential limiting device connected across the current carrying electrodes of the primary winding energizing circuit switching device which limits the reflected primary winding potentials to values at which the ignition coil primary winding switching device will not be damaged or destroyed.

For a better understanding of the present invention, together with additional objects, advantages and features thereof, reference is made to the following description and accompanying drawings in which:

FIG. 1 sets forth the improved internal combustion engine ignition system of this invention in schematic form;

FIG. 2 is a curve of the ignition spark potential produced by the circuit of FIG. 1; and

FIG. 3 is a 8-H curve for a typical ignition coil magnetic core iron.

As point of reference or ground potential is the same point electrically throughout the system, it has been illustrated in FIG. 1 by the accepted schematic symbol and referenced by the numeral 5.

Referring to FIG. 1 of the drawing, the internal combustion engine ignition system of this invention is set forth in schematic form in combination with a source of direct current potential having positive and negative polarity output terminals, which may be the automobile storage battery 10, and an ignition distributor 15 having a movable electrical contact 14, rotated in timed relationship with an associated internal combustion engine l2, through'which the ignition spark potential is applied to the spark plugs of the engine individually, in a manner well known in the automotive art.

The internal combustion engine with which the ignition system of this invention may be used is set forth in block form, is referenced by the numeral 12, and is illustrated as having eight spark plugs 18, 28, 38, 48, 58, 65, 7S and 88, each having an arc gap, as is well known in the automotive art. It is to be specifically understood, however, that the ignition system of this invention may be used with internal combustion engines having more or less cylinders and also with rotary type engines.

To supply operating potential to the system, movable contact 21 of an electrical switch 20 may be closed to stationary contact 22 to place battery potential across lead 23 and point of reference or ground potential 5. Movable contact 21 and stationary contact 22 may be a pair of normally open contacts included in a conventional automotive ignition switch of a type well known in the automotive art. For purposes of this specification, it will be assumed that movable contact 21 is electrically closed to stationary contact 22, as shown in FIG. 1.

The ignition coil 25 has a magnetic core 26, a primary winding 27 which, during the buildup of the flow of an energizing current therethrough, produces a magnetic flux in core 26 and a secondary winding 28 in which an ignition spark potential of a sufficient potential magnitude to initiate an arc across the arc gap of each of the spark plugs of engine 12 is induced upon the interruption of the flow of energizing current through primary winding 27, as is well known in the automotive art. Primary winding 27 is designed to have an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the arc initiated across each spark plug arc gap for a predetermined duration of time and ignition coil 25 has a secondary to primary winding 3 turns ratio which will provide a predetermined rapid ignition spark potential rise time, as will be explained later in this specification.

An electrical switching device having current carrying elements operable to the electrical circuit open and closed conditions connected in series in the ignition coil primary winding energizing circuit is provided. In

' FIG. 1, this electrical switching device is illustrated as an NPN switching transistor 30 having current carrying elements, collector electrode 32 and emitter electrode 33, operable to the electrical circuit open and closed conditions in response to electrical signals applied to the control electrode, base electrode 31, thereof. The collector-emitter electrodes of switching transistor 30 are connected in series in the ignition coil primary winding energizing circuit. The ignition coil primary energizing circuit may be traced from the positive polarity terminal of battery 10 through lead 24, the closed contacts of electrical switch 20, lead 23, primary winding 27 of ignition coil 25, lead 34, the collector-emitter electrodes of switching transistor 30, lead '36 and point of reference or ground potential to the negative polarity terminal of battery 8. The current carrying elements of the ignition coil primary winding energizing circuit switching device, the collector-emitter electrodes of switching transistor 30, are operated to the electrical circuit open condition at the time each spark plug of engine 12 is to be fired in response to each one of a series of ignition signals produced in timed relationship with engine 12 in a manner well known in the automotive art. That is, when the current carrying elements of this switching device are operated to the electrical circuit closed condition, energizing current flows through primary winding 27 of ignition coil 25 through the primary winding energizing circuit previously described and when the current carrying elements are operated to the electrical circuit open condition in response to each ignition signal, the ignition coil primary winding 27 energizing current flow is interrupted and an ignition spark potential is induced in secondary winding 28.

The series of ignition signals may be produced in timed relationship'with engine 12 by any one of the several conventional'magnetic distributors well known in the automotive art. One example of a magnetic distributor well known in the automotive art suitable for use with the ignition system circuit of this invention is of the variable reluctance type disclosed and described in US. Pat. No. 3,254,247, Falge, which issued May 31, 1966 and is assigned to the same assignee as that of the present invention. In the interest of reducing drawing complexity, the variable reluctance type ignition distributor disclosed and described in US. Pat. No. 3,254,247 has been set forth in schematic form in the drawing. A rotor member 16 is rotated in timed relationship with the engine by the engine in a manner well known in the automotive art within the bore of pole piece 17. Equally spaced about the outer periphery of rotor 16 and about the bore of pole piece 17 are a series of projections equal in number to the number of cylinders of the engine with which the distributor and ignition system is being used. Pole piece 17 may be made up of a stack of a number of laminations of magnetic material secured in stacked relationship by rivets or bolts or other fastening methods and the magnetic v flux may be provided by a permanent magnet, not

shown, which may be secured to the lower face surface thereof. As each projection on rotor member 16 approaches a projection on pole piece 17, the reluctance of the magnetic path between pole piece 17 and rotor 16 decreases and as each projection on rotor 16 moves away from a projection on pole piece 17, the reluctance of the magnetic circuit between pole piece 17 and rotor 16 increases. Consequently, the magnetic field produced by the permanent magnet increases and decreases as each projection on rotor 16 approaches and passes a projection on pole piece 17, a condition which induces an alternating current potential in pickup coil 18, which is magnetically coupled to pole piece 17, of a wave-form as shown in FIG. 1.

To operate the current carrying elements of the electrical switching device, the collector-emitter electrodes of switching transistor 30, to the electrical circuit closed and open conditions in timed relationship with engine 12, an electronic ignition system 35 responsive to the series of ignition signals induced in pickup coil 18 is provided. One example of an electronic ignition system suitable for use with this invention is set forth schematically in FIG. 1. During each positive polarity excursion of the series of ignition signals induced in pickup coil 18, terminal end thereof is of a positive polarity with respect to terminal 18b, consequently, diode 43 is reverse biased. While diode 43 is reverse biased, base-emitter drive current is supplied to NPN transistor 40 from the positive polarity terminal of battery 10, through lead 24, the closed contacts of switch 20, lead 23, resistors 44 and 45, the base-emitter electrodes of transistor 40, resistor 46 and point of reference or ground potential 5 to the negative polarity terminal of battery 10. While base-emitter drive current is supplied to NPN transistor 40, this device conducts through the collector-emitter electrodes thereof. While transistor 40 conducts through-the collector-emitter electrodes, the potential upon junction 47 is of an insufficient potential magnitude to produce a baseemitter drive current through NPN transistor 41, consequently, transistor 41 is not conductive. While transistor 41 is not conductive, base-emitter drive current is supplied to NPN transistor 42 from the positive polarity terminal of battery 10, through lead 24, the closed contacts of switch 20, lead 23, resistors 48 and 49, the'base-emitter electrodes of transistor 42, lead 50, the base-emitter electrodes of switching transistor 30, lead 36 and point of reference or ground potential 5 to the negative polarity terminal of battery 10. While base-emitter'drivecurrent is supplied to NPN transistor 42, this device conducts through the collector-emitter electrodes. While transistor 42 conducts through the collector-emitter electrodes, base-emitter drive current is supplied to NPN switching transistor 30 from the positive polarity terminal of battery 10, through lead 24, the closed contacts of switch 20, lead 23, resistor 51, the collector-emitter electrodes of transistor 42, lead 50, the base-emitter electrodes of switching transistor 30, lead 36 and point of reference or ground potential 5 to the negative'polarity terminal of battery 10. While base-emitter drive current is being supplied to switching transistor 30, this device conducts through the collector-emitter electrodes to complete the ignition coil primary winding energizing circuit previously described. During the next negative polarity excursion of the series of ignition signals induced in pickup coil 18, terminal end 180 thereof is .of a negative polarity with respect to terminal end 18b, consequently, diode 43 is forward biased. At the moment diode 43 becomes forward biased at the beginning of each negative polarity excursion of the ignition signals, base-emitter drive current is diverted from transistor 40 to extinguish this device. With transistor 40 not conducting, base-emitter drive current is supplied to transistor 41 from the positive polarity terminal of battery 10, through lead 24, the closed contacts of switch 20, lead 23, resistors 52 and 53, the base-emitter electrodes of transistor 41, resistor 46 and point of reference or ground potential 5 to the negative polarity terminal of battery 10. While base-emitter drive current is being supplied to switching transistor 30, this device conducts through the collector-emitter electrodes to complete the ignition coil primary winding energizing circuit previously described. During the next negative polarity excursion of the series of ignition signals induced in pickup coil 18, terminal end 18a thereof is of a negative polarity with respect to terminal end 18b, consequently, diode 43 is forward biased. At the moment diode 43 becomes forward biased at the beginning of each negative polarity excursion of the ignition signals, base-emitter drive current is diverted from transistor 40 to extinguish this device. With transistor 40 not conducting, base-emitter drive current is supplied to transistor 41 from the positive polarity terminal of battery 10, through lead 24, the closed contacts of switch 20, lead 23, resistors 52 and 53, the base-emitter electrodes of transistor 41, resistor 46 and point of reference or ground potential 5 to the negative polarity terminal of battery 10. While base-emitter drive current is being supplied to transistor 41, this device conducts through the collectoremitter electrodes to drain base drive current from transistor 42, consequently, transistor 42 extinguishes. When transistor 42 extinguishes, base-emitter drive current is no longer supplied to switching transistor 30, consequently, switching transistor 30 extinguishes to interrupt the ignition coil primary winding energizing circuit. Upon each interruption of the ignition coil primary winding energizing circuit, an ignition spark potential is induced in secondary winding 28 which is di- ,rected to the next spark plug of engine 12 to be fired through the movable contact 14 of distributor 15, in a manner well known in the automotive art.

In a practical application of the internal combustion engine ignition system of this invention, the electronic ignition systems disclosed and described in detail in US. Pat. No. 3,605,713, LeMasters et al, issued Sept. 20, 1971, and in US. Pat. application Ser. No. 390,882, Richards et al., filed Aug. 23, 1973, both of which are assigned to the same assignee as is this invention, were employed.

The rise time of the ignition spark potential E induced in the ignition coil secondary winding, hereinafter referred to as rise time, is determined by the frequency of the ignition spark potential E, induced in the secondary winding upon the interruption of the energizing circuit of the ignition coil primary winding, the higher the frequency the faster the rise time. The ignition spark potential E, induced in the secondary winding increases substantially sinusoidally, consequently, the frequency thereof is equal to the reciprocal of the product of 2 1t and the square root of the product of the secondary inductance L and the secondary capacitance C,, as expressed by the formula:

f 1/2 1r V L,C, cycles per second The secondary inductance L, is made up of the inductance of the ignition coil secondary winding and the extremely small inductance of the spark plug leads which may be disregarded. Consequently, the inductance value of the secondary winding will be considered to be the secondary inductance L, The secondary capacitance C, is made up of the ignition coil secondary winding interwinding and interlayer capacitance, the capacitance of the spark plug leads, the spark plug capacitance and other stray capacitances. For any ignition system, therefore, the value of the secondary capacitance C, is substantially constant, typically of the order of picofarads (90 X 10 farads). Therefore, to increase the frequency of the ignition spark potential E, induced in the ignition coil secondary winding, the ignition coil secondary winding inductance L must be decreased. The duration of the ignition arc, hereinafter referred to as arc duration, is determined by the energy W stored in the ignition coil primary winding, the greater the stored energy the longer the arc duration. The energy W stored in ignition coil primary winding is equal to one-half the product of the primary winding inductance L and the square of the primary winding energizing current I,,, as expressed by the formula:

W, L (I /2 joules tance of the ignition coil primary winding L and the square of the secondary winding to primary winding turns ratio N lN hereinafter referred to as the turns ratio, as expressed by the formula:

(III) From this formula, it is apparent that the lower the turns ratio, the lower is the value of the secondary winding inductance L and, from Formula I, the higher the frequency of the ignition spark potential E, induced in the ignition coil secondary winding. That is, an ignition coil suitable for use as a portion of the ignition system of this invention must have a primary winding of a sufficient inductance value which, with maximum energizing current flow therethrough as determined by the current carrying and interrupting capabilities of the energizing circuit switching device, will store sufficient energy W,, to provide the desired arc duration and a turns ratio low enough to provide the desired rise time.

In any ignition system, the fixed parameters are the maximum ignition coil primary winding energizing current, as determined by the current carrying and interrupting capabilities of the ignition coil primary winding energizing circuit switching device, and the maximum primary winding potential E at the moment the primary winding energizing circuit is interrupted upon the 7 operation of the switching device to the electrical circuit open condition, as determined by the maximum potential the ignition coil primary winding energizing circuit switching device is capable of withstanding without damage or destruction. For purposes of illustrating the steps in the design of an ignition coil suitable for use as a portion of the ignition system of this invention, it will be assumed that the ignition coil primary winding energizing circuit switching device is NPN transistor 30, that the maximum current carrying and interrupting capabilities of transistor 30 is 5.5 amperes and that the maximum potential which may be applied across the collector-emitter electrodes thereof, the maximum primary winding potential E,, at the moment of primary winding energizing circuit interruption, is 500 volts. Further, it will be assumed that the desired rise time of the ignition spark potential E, induced in secondary winding 28 be 40 microseconds from zero to the order of 30 kilovolts and that the arc duration be 800 micromicroseconds.

At the moment of the interruption of the energizing circuit of ignition coil primary winding 27, the ignition spark potential E, induced in secondary winding 28 is equal to the product of the primary winding potential E and the turns ratio, as expressed by the formula:

E, E, (N /N volts (IV) As the maximum primary potential E which transistor 30 may withstand without damage or destruction is 500 volts and it is desired that the ignition spark potential E induced in secondary winding 28 be of the order of at least 30 kilovolts, by substituting a value of 30 kilovolts for E, and 500 volts for E in Formula IV and solving for the turns ratio N /N it is found that ignition coil 25 must have a turns ratio of 60:].

Primary winding 27 must have an inductance L value which, with the maximum ignition coil primary winding energizing current flow of 5.5 amperes, will have sufficient stored energy W to provide the ionization energy W, required to ionize the arc gap of the spark plug to which it is directed and strike the ignition arc, the arc duration energy W required to maintain the are for 800 microseconds and the system loss energy W required to make up for the system energy losses. The ionization energy W and the arc duration energy W are determined by the following respective formulas:

t (E) C /2 joules W E I (arc duration)/2 joules (V!) where:

E, Potential required to ionize each spark plug arc gap and strike the arc C Secondary capacitance E Potential required to maintain the ignition arc I Secondary current in amperes In a practical application of the internal combustion engine ignition system of this invention, the secondary capacitance was 90 picofarads (90 X 10' farads), the potential E,- required to ionize each spark plug arc gap and strike the ignition arc was 15 kilovolts, the potential E required to maintain the arc was 1.2 kilovolts and the system energy W losses were equal to approximately 0.4 the secondary winding energy W The secondary current I, is equal to the primary current 1,, divided by the turns ratio and multiplied by a loss factor, which was found to be approximately 0.80, as expressed by the formula:

I .8 milliamperes ization energy W required to ionize each spark plug arc gap and strike the ignition arc is 10.125 millijoules.

(VII) To determine for the required are duration energy W a value of 1.2 kilovolts is substituted for E,,, a value of milliamperes is substituted for I, and 800 microseconds is substituted for (arc duration) in Formula VI. Solving for the arc duration energy W it is found that the arc duration energy W required to maintain the arc 800 microseconds is 36 millijoules. The total secondary energy W, required, is the total of the ionization energy W,, the arc duration energy W and the loss energy W,, as expressed by the formula:

W, W,- W,, W, millijoules (VIII) As the loss energy was determined to be approximately 0.4 W,, by substituting 10.125 millijoules for W,, 36 millijoules for W and 0.4 W for W, in Formula VIII and solving for the total secondary W it is found that the total secondary energy W, required is 76.875 millijoules.

In a practical application of the internal combustion engine ignitionsystem of this invention, itwas found that the transfer of energy from the primary winding 27 to the secondary winding 28 was approximately 70 percent. The required primary energy W to be stored in primary winding 27, therefore, is determined by the formula:

W W /0.7 millijoules By substituting a value of 76.875 millijoules for the secondary energy W, in this formula and solving for the primary winding energy W it is found that the required primary winding energy W is millijoules.

The primary winding inductance L is equal to two times the primary winding energy W divided by the square of the primary winding energizing current I,,, as expressed by the formula:

L 2W /(I 2 millihenries v By substituting 1 l0 millijoules for the primary winding energy W and 5.5 amperes for the primary current Ip in Formula X and solving for the primary winding inductance L,,, it is found that the primary inductance L required to produce sufficient energy W,, stored in L, L,, X (hi /N henries By substituting the previously calculated primary inductance L,,, 8 millihenries, and the turns ratio 60 in Formula XI and solving for the secondary inductance L it is found that the secondary inductance L, is 28.8 henries.

To calculate the frequency of the ignition spark potential E, induced in ignition coil secondary winding 28 upon the interruption of the primary winding energizing circuit, a value of 28.8 millihenries is substituted for L, and a value of 90 picofarads (90 X 10' farads) is substituted for C, in Formula I. The solution of this formula indicates that the frequency of the potential induced in secondary winding 28'is 3,120 cycles per second, consequently, the period of each cycle (l/f) is 320 E} 2W,/C kilovolts (X11) By substituting the value 76.875 for W, and 90 picofarads (90 X 10 farads) for C, in Formula XII and solving for the available voltage E it is found that the available voltage or the peak voltage which may be provided by secondary winding 28 is of the order of 42 kilovolts. As the potential induced in secondary winding 28 is substantially a sine wave, the value of this induced potential 30,45 and 60 may be calculated by multiplying the maximum available voltage E, by the sine of 30, 45 and 60. These points may be plotted on a curve, FIG. 2, having degrees and milliseconds on the X axis and kilovolts on the Y axis. As the induced potential initially goes negative, the curve of FIG. 2 is plotted in the second quadrant. It may be noted that, the available maximum potential E reaches approximately 30 kilovolts in 40 microseconds.

The actual number of primary windings is determined by the magnetic properties of the iron employed in magnetic core 26 of ignition coil 25. For purposes of this specification, a typical B-H curve for magnetic iron employed as ignition coil magnetic cores is set forth in FIG. 3. It is desirable, if not necessary, to operate on the linear portion of this curve which indicates that a flux density B of 75,000 lines per square inch is located on the linear portion of the curve and just prior to the break point or knee. In a practical application of the internal combustion engine ignition system of this invention, core 26 had a cross-section area of 0.5 square inch. The number of primary turns is equal to the product of the primary inductance L and the primary winding energizing current 1 divided by the number of lines per square inch, as expressed by the formula:

xm) By substituting the required primary inductance, 8 henries, the maximum primary current 1,,, .5 amperes, and the number of lines per square inch of core area, 37.5 X in Formula XIII and solving for the primary turns N it is found that 118 primary turns are required. As the secondary winding to primary winding turns ratio is 60: 1, a total of 7,080 secondary turns are required.

volts (XIV) the current carrying elements of the ignition coil primary winding energizing current switching device, transistor 30. The metal oxide varistor is a commercially available item marketed by the General Electric Company. With this device, the maximum potential which will appear across the ignition coil primary winding energizing circuit switching device is the breakdown potential of the metal oxide varistor employed, in

this case 500 volts. Therefore, metal oxide varistor 60 serves as a protective device which prevents the damage to or destruction of switching transistor 30 under abnormal operating conditions such as an electrically open ignition coil secondary winding 28 output circuit.

For purposes of illustrating the novel internal combustion engine ignition system of this invention, it was assumed, in this specification, that an internal combustion ignition system having an arc duration of 800 microseconds and an ignition spark potential rise time of 40 microseconds from zero to 30 kilovolts was required. It is to be specifically understood that other arc duration and rise time values may be selected, as desired or as determined by the application, without departing from the spirit of the invention. Typically, thearc duration may be within a range of 700 1,800 microseconds, inclusive, the turns ratio may be within a range of 40:1 to 60:1, inclusive, and the rise time of the ignition spark potential induced in the ignition coil secondary winding may be within a range of 30 45 microseconds.

Prior art systems, such as that represented by U.S. Pat. No. 3,264,521, Huntzinger et al., issued Aug. 2, 1966, and assigned to the same assignee as is this invention, employ Zener diode devices for the purpose of protecting a switching device against intolerable transient potential spikes which may be produced in a normal operating ignition system. The novelty of the internal combustion engine ignition system of this invention is not directed to the metal oxide varistor alone or the use of this device or any other device having similar electrical characteristics to provide transient protection for the ignition coil primary winding energizing cir-.

cuit switching transistor but is directed to the complete ignition system combination of an ignition coil specifically designed to have a primary winding inductance of a sufficient value to provide a desired arc duration and a turns ratio low enough to provide a fast or rapid rise time ignition spark potential in combination with a primary winding potential limit device which prevents damage to or destruction of the ignition coil primary winding energizing circuit switching transistor w'ithabnormal ignition coil secondary winding output circuit open conditions.

While a preferred embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that various modifications and substitutions may be made without departing from the spirit of the invention which is to be limited only within the scope of the appended claims.

What is claimed is:

1. An internal combustion engine ignition system comprising in combination with a source of direct current potential having positive and negative polarity output terminals; an ignition coil having a magnetic core, a primary winding which, during the buildup of the flow of energizing current therethrough, produces a magnetic flux in said core and a secondary winding in which an ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, willprovide sufficient stored energy to maintain the ignition are initiated across each spark plug arc gap for a predetermined duration of time and said ignition coil having a secondary to primary winding turns ratio selected to provide an ignition spark potential of a predetermined rapid rise time; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; an electrical switching device having current carrying elements operable to the electrical circuit closed and open conditions connected in series in said ignition coil primary winding energizing circuit; means for operating said current carrying elements of said electrical switching device to the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said current carrying elements of said electrical switching device.

2. An internal combustion engine ignition system comprising in combination with a source of direct cur- P 3! pot tl ia h v ng. Pos iv an n a n put terminals; an ignition coil having a magnetic core, a primary winding which, during the buildup of the flow of energizing current therethrough, produces a magnetic flux in said core and a secondary winding in which an ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the ignition arc initiated across each spark plug arc gap for a predetermined duration of time and said ignition coil having a secondary to primary winding turns ratio selected to provide an ignition spark potential of a predetermined rapid rise time; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; a transistor switching device having the collectoremitter electrodes thereof connected in series in said ignition coil primary winding energizing circuit; means for operating said collector-emitter electrodes of said transistor switching device to. .'the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said collectoremitter electrodes of said transistor switching device.

3. An internal combustion engine ignition system comprising in combination with a source of direct current potential having positive and negative polarity output terminals; an ignition coil having a magnetic core, a primary winding which, during the buildup of the flow of energizing current therethrough, produces a magnetic flux in said core and a secondary winding in which an ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the ignition arc initiated across each spark plug arc gap for a duration of time of the order of 800 microseconds and said ignition-coil having a secondary to primary winding turns raio of the order of :1 to provide an ignition spark potential of a rapid rise time of the order of 40 microseconds; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; an electrical switching device having current carrying elements operable to the electrical circuit closed and open conditions connected in series in said ignition coil primary winding energizing circuit; means for operating said current carrying elements of said electrical switching device to the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said current carrying elements of said electrical switching device.

4. An internal combustion engine ignition system comprising in combination with a source of direct current potential having positive and negative polarity output terminals; an ignition coil having a magnetic core, a primary winding which, during the buildup of the flow of energizing r n there o h prpd e a netic flux in said core and a secondary winding in which an ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the ignition arc initiated across each spark plug arc gap for a duration of time within a range of 700 1,800 microseconds, inclusive, and said ignition coil having a secondary to primary winding turns ratio within a range of 40:1 to 60:1, inclusive, to provide an ignition spark potential of a rapid rise time within a range of 30 45 microseconds, inclusive; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; an electrical switching device having current carrying elements operable to the electrical circuit closed and open conditions connected in series in said ignition coil primary winding energizing circuit; means for operating said current carrying elements of said electrical switching device to the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said current carrying elements of said electrical switching device.

5. An internal combustion engine ignition system comprising in combination with a source of direct current potential having positiveand negative polarity output terminals; an ignition coil having a magnetic core,

a primary winding which, during the buildup of the flow of energizing current therethrough, produces a magnetic flux in said core and a secondary winding in which an ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the ignition arc initiated across each spark plug arc gap for a duration of time within a range of 700 1,800 microseconds, inclusive, and said ignition coil having a secondary to primary winding turns ratio within a range of 40:1 to 60:1, inclusive, to provide an ignition spark potential of a rapid rise time within a range of 30 45 microseconds, inclusive; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; a transistor switching device having the collectoremitter electrodes thereof connected in series in said ignition coil primary winding energizing circuit; means for operating said collector-emitter electrodes of said transistor switching device to the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said collectoremitter electrodes of said transistor switching device. 

1. An internal combustion engine ignition system comprising in combination with a source of direct current potential having positive and negative polarity output terminals; an ignition coil having a magnetic core, a primary winding which, during the buildup of the flow of energizing current therethrough, produces a magnetic flux in said core and a secondary winding in which an ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the ignition arc initiated across each spark plug arc gap for a predetermined duration of time and said ignition coil having a secondary to primary winding turns ratio selected to provide an ignition spark potential of a predetermined rapid rise time; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; an electrical switching device having current carrying elements operable to the electrical circuit closed and open conditions connected in series in said ignition coil primary winding energizing circuit; means for operating said current carrying elements of said electrical switching device to the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said current carrying elements of said electrical switching device.
 2. An internal combustion engine ignition system comprising in combination with a source of direct current potential having positive and negative polarity output terminals; an ignition coil having a magnetic core, a primary winding which, during the buildup of the flow of energizing current therethrough, produces a magnetic flux in said core and a secondary winding in which An ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the ignition arc initiated across each spark plug arc gap for a predetermined duration of time and said ignition coil having a secondary to primary winding turns ratio selected to provide an ignition spark potential of a predetermined rapid rise time; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; a transistor switching device having the collector-emitter electrodes thereof connected in series in said ignition coil primary winding energizing circuit; means for operating said collector-emitter electrodes of said transistor switching device to the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said collector-emitter electrodes of said transistor switching device.
 3. An internal combustion engine ignition system comprising in combination with a source of direct current potential having positive and negative polarity output terminals; an ignition coil having a magnetic core, a primary winding which, during the buildup of the flow of energizing current therethrough, produces a magnetic flux in said core and a secondary winding in which an ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the ignition arc initiated across each spark plug arc gap for a duration of time of the order of 800 microseconds and said ignition coil having a secondary to primary winding turns raio of the order of 60:1 to provide an ignition spark potential of a rapid rise time of the order of 40 microseconds; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; an electrical switching device having current carrying elements operable to the electrical circuit closed and open conditions connected in series in said ignition coil primary winding energizing circuit; means for operating said current carrying elements of said electrical switching device to the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said current carrying elements of said electrical switching device.
 4. An internal combustion engine ignition system comprising in combination with a source of direct current potential having positive and negative polarity output terminals; an ignition coil having a magnetic core, a primary winding which, during the buildup of the flow of energizing current therethrough, produces a magnetic flux in said core and a secondary winding in which an ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the ignition arc initiated across each spark plug arc gap for a duration of time within a range of 700 - 1,800 microseconds, inclusive, and said ignition coil having a secondary to primary winding turns ratio within a range of 40:1 to 60:1, inclusive, to provide an ignition spark potential of a rapid rise time within a range of 30 - 45 microseconds, inclusive; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; an electrical switching device having current carrying elements operable to the electrical circuit closed and open conditions connected in series in said ignition coil primary winding energizing circuit; means for operating said current carrying elements of said electrical switching device to the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said current carrying elements of said electrical switching device.
 5. An internal combustion engine ignition system comprising in combination with a source of direct current potential having positive and negative polarity output terminals; an ignition coil having a magnetic core, a primary winding which, during the buildup of the flow of energizing current therethrough, produces a magnetic flux in said core and a secondary winding in which an ignition spark potential of sufficient magnitude to initiate an ignition arc across the arc gap of each of the spark plugs of the engine is induced upon the interruption of the flow of energizing current through said primary winding, said primary winding having an inductance value which, with a predetermined magnitude of energizing current, will provide sufficient stored energy to maintain the ignition arc initiated across each spark plug arc gap for a duration of time within a range of 700 - 1,800 microseconds, inclusive, and said ignition coil having a secondary to primary winding turns ratio within a range of 40:1 to 60:1, inclusive, to provide an ignition spark potential of a rapid rise time within a range of 30 - 45 microseconds, inclusive; an ignition coil primary winding energizing circuit through which energizing current flows from said source of direct current potential through said ignition coil primary winding; a transistor switching device having the collector-emitter electrodes thereof connected in series in said ignition coil primary winding energizing circuit; means for operating said collector-emitter electrodes of said transistor switching device to the electrical circuit closed and open conditions in timed relationship with the associated internal combustion engine; and a metal oxide varistor connected in shunt across said collector-emitter electrodes of said transistor switching device. 